1. Field of the Invention
The present invention relates to a zoom lens system that is provided for imaging.
2. Description of Related Art
Due to the rapid popularization of digital cameras in recent years, lower-priced digital cameras have been in demand, and also there has been a strong demand for price reduction in regard to photographic optical systems. Furthermore, in compact digital cameras, there is a tendency for excellent portability to be desired, so that attempts are made to further miniaturize and slim down the digital camera. On the other hand, the number of pixels of solid-state image sensors, such as CCDs, etc., is increasing year by year. Accordingly, a high-quality photographic optical system that can cope with such fineness of pixel pitch is in demand.
A negative-lead zoom lens system is utilized as a zoom lens system for use in a compact digital camera having a zoom ratio of approximately 3:1 through 4:1. For example, Japanese Unexamined Patent Publication Nos. 2005-084597 and 2009-092740 both disclose a negative-lead zoom lens system having a negative lens group, a positive lens group and a positive lens group, in that order from the object side, i.e., a zoom lens system having three lens groups, in which a zoom ratio of approximately 3.7:1 is achieved.
However, the overall length of these optical systems and the thickness of each lens group are large, and hence do not satisfy the requirements for miniaturization. In order to achieve miniaturization of a camera at a non-photographable state, it is necessary for the overall length of the lens system to be reduced and for the thickness of each lens group to be made thinner. In order to shorten the overall length of the lens system, the refractive power of each lens group can be strengthened and the amount movement thereof during zooming can be reduced; however, the amount of aberrations occurring at the refractive surfaces of the lens elements increases so that aberration correction thereof becomes difficult. Moreover, the market demands such lens systems to be further miniaturized while attaining a higher zoom ratio and a higher optical quality.